What about regular popsicles? My doc suggested them for ME when I was pregnant with a bout of gastroenteritis... and he didn't want to hospitalize me for dehydration. Get the plain old orange, cherry or grape ones that are singles. They taste better than those nasty pedialyte ones.
And you can make it into a game/treat. "Look! Mommy got us some popsicles! I'm having __, what flavor do you want?"
If he likes bananas... there ARE some banana flavored ones out there (and they are pretty good).. but you will have to look for them.. they are off brand.. not Popsicle brand.
Oh... and gingerale~
That was always what my mom gave us when we were sick. The ginger helps settle the stomach too... maybe the "fizz" will get him to want to try it. Just tiny sips though. At this point... don't worry about the "electrolyte" content.. just get fluid in him! Smartwater and Vitamin water have electrolytes (and B vitamins in the vitamin water) if you want to try one of those. They have NO artificial sweeteners nor high fructose corn syrup and are less syrupy sweet than most gatorade or powerade drinks too. Lots of flavors to try...